Custom circuit drives a small round CRT display

[Svofski’s] latest hack seeks to do no more than look cool on his desk. We’d say mission accomplished. He doesn’t even need anyone around to be proud of the small round CRT display unit he put together. Just having it hum away next to him will be more than enough to keep him going when regular work gets a bit tedious.

One of the biggest challenges when working with a cathode ray tube is the supply. He compares the requirements with that of Nixie tubes, and this is quite a bit more challenging since he wants to generate the 750V from a 12V DC source. To pull it off he hand wound his own transformer. There are two secondary coils, one for the cathode heater and the other as the supply. You can see a brief clip of the unit in action after the break.

Take note of the PCB section of his writeup. He took a meandering route through several different software packages before printing the board. It started with Eagle, moved to freerouting.net, which produced a Specctra file that he converted to gEDA using a Python script.

It would be ignored (indiscernible) if buried in a bag of adaptors. I have gotten my large hand-wired led panels through without pause, even a Geiger counter I forgot was in my carry on. They don’t care.

though this particular project likely wouldn’t lay you flat, standard commonsense rules still apply… (keep one hand behind your back, for instance, when coming into contact with the high volatge portions of the circuit if they’re live)

A defibrillator applies 200 joules at 1000 volts in 5 milliseconds. This works out to 40 amps. This seems like it would be a lot for a little power supply like this (unless it has some insane capacitors). However I could see places where less energy could be applied causing more damage so take it with a grain of salt.

How about those electric fly swatters? I stupidly measured one at 1100 volts and then burned out a cheap dvm trying to measure another.

A few years back, I had a broken swatter. Just the handle with a couple wires sticking out. I did not realize one of the wires was disconnected. So when I shorted the leads to discharge it, it did not actually discharge. Moments later I was futzing with the wires, one in each hand.. you know where this is going.. I took the stored charge through the arms and across my upper torso. Not fun!

The one I had was no more than 1000V. That was the rating of the capacitor when I opened it up after it broke. My favorite part about it when I was younger was that I could stun flies without actually killing them. Was always fun to baffle people with the fly on a string trick.

Ahh… I had a feeling it was at least on the west coast… I have been planning to visit Astoria, but I think Portland is a very long drive around the cove to get there, if I am not mistaken.

I would love to visit his shop, though, and it does seem that most of the “abundant” outlets for surplus electronics don’t publish their inventory on the internet, probably because there is too much stuff to even get started listing online….

Heh, this is not a Tesla coil, just a modest CRT tube, there are no sparks flying around and it does not smell of ozone :) If there was RF interference capable of making this to the mic, the tube would not be able to form any clear picture. In the writeup I mention that the toroidal transformer does a great job of containing most of the magnetic field very close to itself. People using E-cores usually report interference problems, especially with these tiny tubes.

The sound is me squeezing the phone while filming with it in some uncomfortable position, trying not to shake it too much.